• 한국자기학회지
• /
• 제26권3호
• /
• pp.86-91
• /
• 2016

BLDC 전동기의 코깅토크는 영구자석과 철심의 상호작용에 의해 발생하고 소음과 진동을 발생시키는 요인이다. 제조 과정에서 조립 공차로 인해 영구자석이 회전자 철심 면에 제대로 붙지 않을 경우 BLDC 전동기의 전자기적 구조가 변할 수 있다. 본 논문에서는 조립 공차로 인해 자석이 회전자 표면과 분리되었을 때 코깅토크에 미치는 영향에 대해 연구했다. 핵심적인 설계 요소들인 회전자와 자석 간 분리, 분리를 가진 자석 수, 이웃한 자석들 간의 여러 배치형태를 고려했다. 코깅토크 해석을 위해 유한요소법을 사용하였고, 소음진동을 발생시키지 않는 조립 공차를 제안했다. 제안된 조립 공차로 제작된 BLDC 전동기의 코깅토크는 감소되었고 소음진동 또한 줄어들 것이라고 판단된다.

• 대한기계학회논문집A
• /
• 제36권5호
• /
• pp.537-543
• /
• 2012

본 연구는 운전조건 하에서 감속기 내부기어의 가공정밀도와 소음의 연관 특성에 관한 실험적 연구이다. 이를 위하여 유성기어열로 이루어진 감속기를 제작하였으며, 내부 기어는 정밀도를 다르게 가공한 기어로서 4 세트를 제작하여 비교 실험하였다. 감속기에 대한 소음 및 진동 신호는 신호분석법에 의해 채집되었으며, 정지상태로부터 운전 가능 최고 속도까지 균등하게 증속하며 신호를 채집하였다. 또한 소음 레벨은 소음계를 이용하여 측정하여 비교하였다. 기어의 가공정밀도에 대한 평가는 한국 산업기술 시험원(ktl)에 의뢰하여 일본공업규격(JIS)에 준하여 객관적으로 평가되었으며, 이를 소음, 진동 신호와 함께 비교 분석하였다.

• 한국환경보건학회지
• /
• 제45권6호
• /
• pp.658-667
• /
• 2019

Objective: This study was designed to compare construction types and seasonal radon concentrations in dwellings in Jeollabuk-do Province in Korea. Methods: The measurement of indoor radon concentrations in 79 dwellings using alpha-track detectors was performed every three months (seasonally) over one year between 2015 and 2016. Also, Radon concentrations in soil were measured in spring to investigate the correlations between the concentrations in soil and indoor air. Results: The annual average concentration of indoor radon for dwellings was 89.7±72.1(GM: 72.4) Bq/㎥, with a range (min-max) of 17.2 to 505.4 Bq/㎥. The highest indoor radon concentration was measured in winter and the lowest was shown in summer. The geometric mean of radon concentration in winter was 1.03-2.58 times higher than other seasons. Radon concentrations in soil were investigated at the depth of 1 m, and the concentrations ranged from 1,780 Bq/㎥ to 123,264 Bq/㎥. This showed low correlations with indoor radon concentrations.

• 한국정보통신학회논문지
• /
• 제19권1호
• /
• pp.61-68
• /
• 2015

다양한 종류의 잡음에 의해서 발생하는 음성인식 성능 저하를 보상하기 위해서는 잡음제거가 필수적이다. 마이크로폰 배열을 이용하는 많은 잡음제거 기술 중에서, GSC는 비정상성 잡음을 제거하기 위해서 널리 적용되어 왔다. GSC의 성능은 AMC에 의해서 직접적인 영향을 받는다. 즉, 정확한 목표 음성 신호의 검출은 순수 잡음구간에서의 충분한 잡음제거 및 목표 음성구간에서의 적은 왜곡을 보장하기 위해서 필수적이다. 따라서, 본 논문에서는 고정 빔포밍의 출력과 차단 매트릭스의 출력간의 전력비가 주파수 밴드 단위로 계산되는 향상된 AMC 설계법을 제안한다. 그 후, 밴드별 전력비는 가우시안 혼합에 의해서 각 클래스가 확률적으로 모델링 된다. 실험결과, 제안한 알고리즘이 ROC 및 출력 SNR 관점에서 더 높은 성능을 보였다.

• 교육시설
• /
• 제10권4호
• /
• pp.5-20
• /
• 2003

The purpose of the research on the noise of educational facilities is to build up pleasant environments by minimizing the influence on the students in the school. This study provides fundamental data for acoustic design by measuring, computer simulation and analyzing the room acoustic characteristics of the lecture room in middle school. For measurement on the factors of room acoustic, RT of lecture room and noise reductions depending on various walls of different structures were measured and analyzed. The lecture system being installed and carried out on the normal lecture room was divided into 4 types-employment of multimedia machines, employment of multimedia machines and loud speakers, employment of loud speaker, and existing verbal speaking-and SPL for each type was measured and analyzed. Based on the measured characteristics of acoustic characteristics for normal lecture room, the problems for environment of noise were understood through computer simulation, applications for improvements of performance for each facility were studied, schemes for improvements of performance by using the effects were presented, necessary fundamental data were secured, and schemes to enhance flexibility on the existing facilities of school against changing educational courses were secured.

• 한국소음진동공학회논문집
• /
• 제23권6호
• /
• pp.485-494
• /
• 2013

This paper deals with experimental evaluation methods for high speed judder on the brake-caliper system. Firstly, two types of brake caliper systems due to the wheel vibration was evaluated. Secondly, the high-speed judder of the brake was also investigated using the subjective rating evaluation in the high-speed road test. These experimental evaluations were carried out by changing the materials of brake pad and the specifications of the brake-corner module. Based upon the test results, a new specification of the brake pad, $15{\times}5$ vertical chamfer, was proposed. The new brake pad showed 3 points, 60 %, improvement in the subjective-rating evaluation comparing with conventional one. Besides, we need to decide properly with judder characteristic of pad material and have to carefully take into consideration other design parameters; caliper, disc, and the braking performance, durability, squeal noise.

• ETRI Journal
• /
• 제37권1호
• /
• pp.77-87
• /
• 2015

In wireless networks, cooperation is necessary for many protocols, such as routing, clock synchronization, and security. It is known that cooperator nodes suffer greatly from problems such as increasing energy consumption. Therefore, rational nodes have no incentive to cooperatively forward traffic for others. A rational node is different from a malicious node. It is a node that makes the best decision in each state (cooperate or non-cooperate). In this paper, game theory is used to analyze the cooperation between nodes. An evolutionary game has been investigated using two nodes, and their strategies have been compared to find the best one. Subsequently, two approaches, one based on a genetic algorithm (GA) and the other on learning automata (LA), are presented to incite nodes for cooperating in a noisy environment. As you will see later, the GA strategy is able to disable the effect of noise by using a big enough chromosome; however, it cannot persuade nodes to cooperate in a noisefree environment. Unlike the GA strategy, the LA strategy shows good results in a noise-free environment because it has good agreement in cooperation-based strategies in both types of environment (noise-free and noisy).

• 한국유체기계학회 논문집
• /
• 제6권4호
• /
• pp.14-20
• /
• 2003

In this study an analysis of the flow characteristics in three types of turbo-fans for a vacuum cleaner was performed by using CFD. The characteristics of three models calculated for various rotating speed for flow rates are obtained and compared with measured data. The mixing plane approach is applied to compute the flow between impeller and diffuser. The results show that the model that is modified to reduce fan noise gives stable flow characteristics in operating range than the original model, with both models show similar performance characteristics at the range of high flow rate. Since in the modified model it takes much longer for an impeller blade to pass a diffuser blade than in the original model, and the peak pressure at BPF can be relieved, it is anticipated that the modified model give much lower noise level with similar performance than the original one, which remains to be verified by unsteady computation and measurements. The good agreement between the predictions and measurement results confirms the validity of this study.

• 소음진동
• /
• 제6권5호
• /
• pp.607-616
• /
• 1996

A combined computational fluid dynamics(CFD)-Kirchhoff method is presented for predicting high-speed impulsive noise generated by a hovering blade. Two types of Kirchhoff integral formula are used; one for the classical linear Kirchhoff formulation and the other for the nonlinear Kirchhoff formulation. An Euler finite difference solver is solved first to obtain the flow field close to the blade, and then this flow field is used as an input to a Kirchhoff formulation to predict the acoustic far-field. These formulas are used at Mach numbers of 0.90 and 0.95 to investigate the effectiveness of the linear and nonlinear Kirchhoff formulas for delocalized flow. During these calculiations, the retarded time equation is also carefully examined, in particular, for the cases of the control surface located outside of the sonic cylinder, where multiple roots are obtained. Predicted results of acoustic far-field pressure with the linear Kirchhoff formulation agree well with experimental data when the control surface is at the certain location(R=1.46), but the correlation is getting worse before or after this specific location of the control surface due to the delocalized nonlinear aerodynamic flow field. Calculations based on the nonlinear Kirchhoff equation using a linear sonic cylinder as a control surface show a reasonable agreement with experimental data in negative amplitudes for both tip Mach numbers of 0.90 and 0.95, except some computational integration problems over a shock. This concliudes that a nonlinear formulation is necessary if the control surface is close to the blade and the flow is delocalized.

• Asian Journal of Atmospheric Environment
• /
• 제9권1호
• /
• pp.22-30
• /
• 2015

This study evaluated road shape and roadside barrier impact on near-road air pollution dispersion using FLUENT computational fluid dynamics (CFD) model. Simulated road shapes are three types, namely at-grade, depressed, and filled road. The realizable k-${\varepsilon}$ model in FLUENT CFD code was used to simulate the flow and dispersion around road. The selected concentration profile results were compared with the wind tunnel experiments. The overall concentration profile results show good agreement with the wind tunnel results. The results showed that noise barriers, which positioned around the at-grade road, decrease the horizontal impact distance (In this study, the impact distance was defined as the distance from road surface origin coordinate to the position whose mass fraction is 0.1.) lower 0.33~0.65 times and change the vertical air pollution impact distance larger 2.0~2.27 times than those of no barrier case. In case of filled road, noise barriers decrease the horizontal impact distance lower 0.24~0.65 times and change the vertical air pollution impact distance larger 3.33~3.55 times than those of no barrier case. The depressed road increase 1.53~1.68 times the vertical air pollution impact distance. It contributes the decrease of horizontal air pollution impact distance 0.32~0.60 times compare with no barrier case.